Process for the preparation of alkyl perfluoroalkyl and aryl iodides

ABSTRACT

HIGH YIELDS OF ALKYL, PERFLUOROALKYL AND ARYL IODIDES ARE PREPARED DIRECTLY FROM THEIR CORRESPONDING CARBOXYLIC ACIDS BY REACTION IN SOLUTION WITH IODINE AND AROYL PEROXIDE OR T-BUTYLPEROXY ISOPROPYL CARB ONATE. THE REACTION IS CONDUCTED AT A TEMPERATURE OF ABOUT 110-125*C. FOR ABOUT TWO TO THREE HOURS IN SOLVENTS SUCH AS 1,3-DICHLOROPROPANE, 1,3-DIBROMOPROPANE AND 1,1,2,2-TETRACHLORODIFLUORETHANE. SOLVENTS SUCH AS 1,2-DICHLOROETHANE AND CARBON TETRACHLORIDE CAN BY USED AS SOLVENTS BUT THEY REQUIRE LONGER REACTION TIMES.

3,652,682 PROCESS FOR THE PREPARATION OF ALKYL, PERFLUOROALKYL AND ARYLIODIDES Leonard S. Silbert, Philadelphia, Pa., assignor to the UnitedStates of America as represented by the Secretary of Agriculture NoDrawing. Original application Feb. 28, 1968, Ser. No. 708,804, nowPatent No. 3,531,535, dated Sept. 29, 1970. Divided and this applicationMar. 23, 1970, Ser.

Int. Cl. C07c 25/04, 76/12 US. Cl 260-612 D 7 Claims ABSTRACT OF THEDISCLOSURE This application is a division of application Ser. No.708,804 filed Feb. 28, 1968, now Pat. No. 3,531,535.

A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for purposes of the United StatesGovernment, with the power to grant sublicenses for such purposes, ishereby granted to the Government of the United States of America.

This invention relates to alkyl, perfluoroalkyl, and aryl iodides andmore specifically to a novel process for preparing these compoundsdirectly from their corresponding carboxylic acids by reaction insolution with iodine and aroyl peroxide or t-butyl perester.

Organic iodides such as cetyl trimethyl ammonium idide and cetylpyridinium iodide that can be prepared by the method of this inventionfind use as disinfectants and germicides. Others, such as cetyl iodidereact with tertiary amines to form tetraalkyl ammonium iodide saltswhich are used as supporting electrolytes in polarography. Iodides arealso used as dyes such as erythrosin and Rose Bengal, as photographicsensitizers such as the cyanine dyes and in compounds of medicalinterest such as thyroxin and iodoform. The iodides also find use asintermediates in the preparation of other compounds. Nucleophilicdisplacement reactions of the iodides yield other compounds such assulfonic acid esters, nitro derivatives and mercaptans.

As described in copending application entitled Process for thePreparation of Alkyl and Aryl Iodides, Ser. No. 708,800, filed Feb. 28,1969, aryl and alkyl iodides can be prepared by decomposition or aroyland acyl peroxides in selected solvent systems. Practical application ofthat process requires solvents which are relatively inert to thereactants yet dissolve them without difiiculty and solvents which haveconvenient boiling points, preferably between 90 and 130 C., so that theperoxide decomposes rapidly and controllably.

While investigating other aspects of that reaction, I unexpectedlydiscovered a new reaction for preparing alkyl, perfluoroalkyl, and aryliodides. In this reaction, peroxide abstracts hydrogen from thecarboxylic acid function and the acyl, perfiuoroacyl, or aroylhypoiodite that is generated decomposes to alkyl, perfluoroalkyl, oraryl iodide, respectively, in accordance with Equation 1 illustrated forbenzoyl peroxide and an aliphatic acid.

nitc States ate t ice An object of this invention is to provide a novelmeans of preparing alkyl, perfluoroalkyl, and aryl iodides directly fromtheir corresponding'carboxylic acids. 7

According to this invention, alkyl, perfiuoroalkyl and aryl iodides areprepared directly from their corresponding carboxylic acids by reactionin solution with iodine and peroxide or perester.

Suitable peroxides for the process are aroyl peroxides such as benzoylperoxide, p,p-t-butyl benzoyl peroxide, toluoyl peroxides, chlorobenzoylperoxides and nitrobenzoyl peroxides. In addition, peresters liket-butylperoxy isopropyl carbonate (BPIC) may be used.

The acids may be aliphatic, perfiuoro aliphatic, aromatic or perfiuoroaromatic.

The reaction is conducted in solvents like 1,3-dichloropropane,l,l,2,2-tetrachlorodifiuorethane (Freon 112) and 1,3-dibromopropaneusing stoichiometric quantities of acid, peroxide and iodine, i.e., 2moles of monobasic acid, 1 mole of aroyl peroxide or 2 moles of BPIC,and 1 mole of iodine. However, yields are improved by using higherratios of iodide. The reactions are depicted by Equation 2 for aroylperoxides and Equation 3 for BPIC.

Theoretically, the isopropoxy radical should also abstract hydrogen, butthis radical being of lower stability than the t-butoxy radical rapidlydecomposes at temperatures above room temperature thereby eliminatingthe isopropoxy radical in the hydrogen abstraction process. Hence thet-butoxy radical serves to remove the hydrogen atom of the carboxylgroup.

When aliphatic acids are reacted with either aroyl peroxide or BPIC,high yields, -90%, of alkyl iodides are obtained. High yields are alsoobtained when aromatic acids are reacted with BPIC.

Carbon tetrachloride and 1,2-dichloroethane can be used as solvents forthe reactions but their lower boiling points require longer times tocomplete the reaction.

Results for conversions of stoichiometric molar ratios of octanoic acidand benzoyl peroxide are recorded in Table I. Iodobenzene as a productof the benzoyl peroxide reaction with iodine is formed together with thealkyl iodide but its yield diminishes with an increase in iodineconcentration amounting to only 2% of the total iodine mixture at a 200%iodine excess.

Benzoyl peroxide reacts with perfiuoroaliphatic carboxylic acids toyield perfluoroalkyl iodides in high yields. For instance, benzoylperoxide and perfluorooctanoic acid reacted with iodine, 50% excess, in1,3-dibromopropane solution to give a 60% yield of perfiuoroheptyliodide. The higher boiling 1,3-dibromopropane was used in place of1,3-dichloropropane to effect easier separation of the product. Benzoylperoxide, perfiuoroaliphatic carboxylic acid and iodine (122:1.5)reacted at C. for 2 hours in 1,3-dibromopropane solution (0.35 molar inbenzoyl peroxide concentration).

The aromatic aroyl peroxides will react with aromatic acids in thepresence of iodine to give a mixture of iodides, one corresponding tothe acid and the other to the peroxide. This is illustrated for a 1:2mole ratio of peroxide in acid in iodine excess) solution of1,3-dichloropropane as follows: (the figures in parentheses are percentiodides formed based on the molar conversion of peroxide) benzoylperoxide and m-chlorobenzoic acid gave iodochlorobenzene (34%) andiodobenzene (38%); benzoyl peroxide and p-nitrobenzoic acid gaveiodonitrobenzene (13%) and iodobenzene p-nitrobenzoyl peroxide andbenzoic acid gave iodonitrobenzene (16%) and iodobenzene (61% benzoylperoxide and anisic acid gave iodanisole (11%) and iodobenzene (32%);benzoyl peroxide and perfluorobenzoic acid gave iodopentafluorobenzene(1.0%) and iodobenzene (21%).

Results of the reaction of BPIC and aliphatic and aromatic acids withiodine are shown in Table II. Higher product yields are obtained whenthe alcohols are distilled off as the reaction proceeds.

with a nitrogen inlet and distillation head. BPIC (10.4 gm. of purity,0.05 ,M) was added, the mixture heated at 125 C. for one hour to distilloff the t-butanol and acetone formed. Reaction was completed at 135 C.for two hours after which the solvent (and some iodine) was distilledunder an increased nitrogen flow. The crude product was dissolved inwarm petroleum ether, some insoluble compound was filtered off and thesolvent and iodine evaporated. Yield of crude product was 16 gms.(theory, 18.3 gms.).

TABLE I.REACTION OF BENZOYL PEROXIDE BAND lz/peroxide:

e Yicld based on peroxide.

TABLE II REAOTION OF BPIC AND ALIPHATIC AND AROMATIC ACIDS WITH IODINEReaction conditions Reactants consumed Molar ratio Temper- Iodide, Acid,I Perester, Time, ature, Acid Acid I Perester percent percent percentpercent hrs C Octanoic 2 1. 6 1 b 26 37 28 44 3 a 2 1. 5 1 b 16 15 88 992 c 2 1. 5 1 b 42 51 72 100 2 d 1 1 1 b 81 125 84 2 d 120-120 1 1 l b 81128 97 2 d 135 0. 5 1 1 f 82 140 93 2 d 135 Benzoic 1 1 1 K 72 130 94 2d e t-Butylperoxy isopropyl carbonate. b Iodoheptane Alcohols notdistilled off as reaction proceeded. d Alcohols distilled off asreaction proceeded, Acid not experimentally determined. f1,8-diiodooctane B Iodobenzene The preparation of heptadecyl iodide asnow described I claun:

is typical of the preparative procedures of this invention using anaroyl peroxide and BPIC.

Benzoyl peroxide procedure Iodine (12.7 g., 0.05 m.), stearic acid (14.2g., 0.05 m.), and benzoyl peroxide (6.05 g., 0.025 m.) were weighed intoa flask equipped with a small distillation head. 1,3-dichloropropane (42mls.) and Freon 112 (25 mls.) were added as co-solvents, the latter tominimize the volume of the higher boiling dichloropropane and tofluidize the semi-dissolved mixture. A homogeneous solution was attainedas the temperature was raised to the boiling point of the Freon whichdistilled with only small losses of iodine. When the temperature reached110 C., heating was continued for a total time of 3 hours. All of thesolvent and some of the benzoic acid was distilled from the mixturewhile the pressure was reduced and heating continued.

An ethereal solution of the residue was treated with sodium sulfitesolution to remove free iodine and the solvent was then evaporated. Thecrude product (20 g.) was eluted with petroleum ether through achromatographic column containing silica gel for separation of the bulkof heptadecyl iodide from residual benzoic acid. Evaporation of the mainfraction gave heptadecyl iodide (17.3 g.; Theory 18.3 g.).Recrystallization from a mixture of acetone (70 ml.) and 95% ethanol (25ml.) at 40 yield pure compound (13.0 g., 71% yield).

t-Butylperoxy isopropyl carbonate (BPIC) procedure Iodine (12.7 gm.,0.05 M) and stearic acid (14.2 gm., (45 mls.) in a round bottom flask(200 mls.) equipped 1. A process for preparing aryl iodides comprisingreacting an aromatic acid selected from the group consisting of benzoicacid m-chlorobenzoic acid, p-nitrobenzoic acid, anisic acid andperfiuorobenzoic acid and an aroyl peroxide selected from the groupconsisting of benzoyl peroxide, p,p'-t-btuyl benzoyl peroxide, tolurylperoxide, chlorobenzoyl peroxide and nitro benzoyl peroxide with iodineis the presence of a solvent selected from the group consisting of1,3-dichloropropane, 1,2-dichloroethane and1,1,2,Z-tetrachlorodifluorethane, 1,3-dibromopropane and carbontetrachloride.

2. The process of claim 1 in which the peroxide is benzoyl peroxide.

3. The process of claim 2 in which the aromatic acid is m-chlorobonzoic.

4. The process of claim 2 in which the aromatic acid is p-nitrobenzoic.

5. The process of claim 2 in which the aromatic acid is anisic acid.

6. The process of claim 1 in which the peroxide is pnitrobenzoylperoxide.

7. The process of claim 6 in which the aromatic acid is benzoic.

References Cited Hammond, J.A.C.S., 72, pp. 3737-3743, 1950. Hammond, etal., J.A.C.S., 72, pp. 4711-4715, 1950. Walling, et al., J.A.C.S., 80,pp 228-233, 1958.

HOWARD T. MARS, Primary Examiner US. Cl. X.R.

260-646, 650 R, 650 F, 652 R, 653 R

